A young male zebra finch learns its song during a sensitive period. The sensory motor phase of song learning is closely correlated to development of a song control nucleus, RA,which receives inputs from two other song control nuclei. We previously found that acetylcholine (ACh) content and the enzyme activity of choline acetyltransferase (ChAT) increase transiently in the RA during a sensitive period of song learning, when RA synapses for two inputs are highly plastic. For this purpose, we have investigated whether muscarinic agonist carbachol would affect phosphoinositide (PI) metabolism in the RA.The male zebra finch at 30 days, 50 days after hatching and adults were used. Carbachol-stimulated PI turnover was examined by measuring the accumulation of [3H]-inositol phosphates from [3H]-inositol labeled synaptoneurosomes of RA,in the presence of lithium. Carbachol increased PI turnover significantly. Carbachol-stimulated PI turnover reached a maximum at 50 days after hatching, and decreased to adult level. These results suggest that ACh affects synaptic plasticity of zebra finch RA during song learning, because PI turnover activate protein kinase C responsible for the phosphorylation of some phosphoproteins, which play a important role in synaptic plasticity.2、Cキナーゼ染色用蛍光プローブRIM-1を用い、CキナーゼのRA内分布を調べたところ、歌の臨界期にRAニューロンの細胞体、樹状突起、神経終末に多量のCキナーゼ発現を観察した。3、Cキナーゼの基質であるGAP-43mRNAは、RAに神経終末を送っているHVcニューロンの細胞体上に、歌の臨界期に一過性に強く発現することを、DigラベルGAP-43mRNA In situハイブリダイゼーションにより明らかにした。我々は、これまでキンカチョウの歌の臨界期に特異的に変化する物質を探した。その結果、ACh量の増大、PIレスポンスの増大、Cキナーゼの発現の増大があることを明らかにした。これらの事実は、AChによって駆動されるPIレスポンスがCキナーゼ酵素活性を増加させ、機能タンパク質のリン酸化を引き起こし、歌学習期のRAシナプス可塑性を制御している可能性を強く示唆している。